The present invention is directed generally to flow control devices, and more particularly to a precision flow control device for use in conjunction with intravenous administration sets or the like wherein accurate control of a low fluid flow rate is required.
Intravenous administration sets, which are widely used in the medical field for injecting blood, nutrient and saline solutions, and other fluids into the human body, normally require an adjustable flow control device for accurately controlling the gravity flow of a fluid being administered from a container suspended above the patent. The requirements imposed on such flow control devices are stringent, since the flow rates through the system are small, typically ranging from 400 ml to 1 ml per hour under a head of approximately 75 cm, and the required accuracy of flow control is often high, particularly where the patient is in a critical condition and an under or over dosage of the fluid being administered may be highly detrimental.
Flow control devices heretofore provided in administration sets have utilized various clamp, lever or roller arrangements for partially crimping the flexible tubing universally used in such sets to restrict the cross-sectional area of the passageway, or lumen, of the tubing. One of the more successful of such compression-type devices consists of a ribbed roller movable along a channel-like housing through which the flexible tubing of the system passes, the opposing wall of the housing being inclined at an angle to the path of the roller so that by varying the position of the roller along the channel the degree of flattening of the tubing, and hence the flow rate through the system, can be controlled. This device is described in U.S. Pat. No. 3,099,429 to C. R. Broman, which is assigned to the present assignee.
One disadvantage of flow control devices of this type is that the flexible tubing of the administration set becomes flattened or otherwise dimensionally deformed as a result of the compression force exerted by the clamp, lever or roller. This deformation may progress with time, with the result that the flow rate in the system changes from the rate initially set, requiring the user to periodically readjust the flow control device if a desired flow rate is to be maintained.
One attempt at overcoming this problem is described in U.S. Pat. No. 3,779,507 to E. W. Clarke. Here it is proposed that a segment of the tubing of the administration set be flattened over a needle-like core of progressively increasing diameter to form a tapering flow-bypass passageway between opposing inside surfaces of the flattened tubing segment. The flattened tubing walls are clamped together to restrict fluid flow to an underlying portion of the tapered passageway, and by moving the clamp along the passageway the cross-sectional area of the operative portion of the flow bypass passage, and hence the flow rate through the system, is controlled. This arrangement has the disadvantage of requiring a high-precision molding operation during manufacture of the administration set for forming the flattened tubing section and the internal bypass passage. During the molding operation the needle-shaped core must be positioned within the tubing with great accuracy, the effectiveness of the flow control being dependent on the accuracy with which the bypass passage is formed in the opposing wall surfaces. Furthermore, in use the flow rate through the administration set nevertheless remains dependent on the cross-sectional area of a passage formed by the same material as the flexible tubing of the administration set, thus not completely avoiding the possibility of changes in cross-sectional area and system flow rate with time.
Accordingly, the present invention is directed to a new and improved flow control device for an administration set or the like which provides more stable flow control.